Reimplement the `touch()` function on Linux to avoid depending on the
`syscall` package, and use the `sys/unix` package instead. This is
slightly higher level, and seems to build on AMD64 and ARM64.
This is a better way to check errors, both semantically (no usually nil is
bad, but nil error is good, so this avoids a mental negation) and for
the reporting by the assert package.
This is not yet working, it's just a direct copy of the Manager of Flamenco
2, with Logrus replaced by Zerolog. The API has been documented in
flamenco-manager.yaml as a starting point for the integration.
